Cellulose, a polyhydroxy compound, forms esters with organic acids, anhydrides, and acid chlorides. Cellulose esters of almost any organic acid can be prepared.
Although the different types of cellulose esters are useful in many applications, cellulose esters are generally restricted in their usefulness by their moisture sensitivity, limited compatibility with other synthetic resins, and relatively high processing temperatures. Cellulose esters of higher aliphatic acids (for example, propionates and butyrates) circumvent these shortcomings with varying degrees of success.
Discovering methods to assist in making the cellulose esters more versatile for a wider variety of uses is desirable. Blending the cellulose esters with other classes of polymers is an option. In the majority of polymeric blends, however, the components tend to phase separate to form heterogeneous, immiscible blends. Only in a limited number of cases do polymers blend to form one-phase, miscible blends. Few miscible blends of cellulose esters with other polymers are known.
Blended polymers are not useful for many applications unless the blend is miscible. This is because immiscible blends have low physical attractive forces across the phase boundaries and suffer from delamination at the phase boundaries. Immiscible blends tend to be turbid which excludes them from many applications. Miscible polymer blends, on the other hand, are desirable because of their optical clarity and strength since they are not phase separated and thus stratification of the polymeric components during or after processing is generally avoided. Consequently, miscible blends are useful in many applications. The miscibility of polymer blends can be identified by many different techniques. For example, the properties of optical transparency (in the absence of crystallinity) and a single glass transition temperature are indicative of miscible blends. Additionally, nuclear magnetic resonance, transmission electron microscopy, and excimer fluorescence are methods by which blends may be examined for miscibility (as discussed in Concise Encyclopedia of Science and Engineering, Ed. J. I. Kroschwitz, published by John Wiley & Sons, Inc., 1990, pp.629-632). As used herein, a miscible blend is defined as a blend of two or more polymers that behaves as a single, homogeneous (solid or liquid) material, exhibiting a single glass transition temperature (hereinafter "T.sub.g ").
It would be highly desirable to find a polymeric component that forms a miscible blend with cellulose ester polymers, thus broadening the range of usage of cellulose esters.